Here is the opinion in Democratic National Committee v. Reagan.
An excerpt from Chief Judge Thomas’ dissent:
“No right is more precious in a free country than that of having a voice in the election of those who make the laws under which, as good citizens, we must live.” Wesberry v. Sanders, 376 U.S. 1, 17 (1964). Our right to vote benefits government as much as it benefits us: a representative democracy requires participation, and the people require representatives accountable to them. Arizona’s electoral scheme impedes this ideal and has the effect of disenfranchising Arizonans of African American, Hispanic, and Native American descent.
Arizona’s policy of wholly discarding—rather than partially counting—votes cast out-of-precinct has a disproportionate effect on racial and ethnic minority groups. It violates § 2 of the Voting Rights Act (“VRA”), and it unconstitutionally burdens the right to vote guaranteed by the First Amendment and incorporated against the states under the Fourteenth Amendment.